Oxygen Uptake and Lactate Kinetics in Patients with Chronic Obstructive Pulmonary Disease during Heavy Intensity Exercise: Role of Pedaling Cadence

Abstract

Oxygen uptake slow component (${\dot{V}}_{{\mathrm{O}}_2}$_sc) is associated with lactate accumulation, likely a contribution of poorly oxidative muscle fibers. We aimed to test the hypothesis that higher muscle tension during slow pedaling rates would yield more prominent ${\dot{V}}_{{\mathrm{O}}_2}$_sc in healthy subjects, but not in COPD patients. Eight severe COPD patients and 8 age-matched healthy individuals performed 4 rest-heavy exercise transitions at 40 and 80 RPM. Work rates at the two cadences were balanced. Venous blood was sampled for measurement of lactate concentration at rest and every 2 minutes until the end of exercise. ${\dot{V}}_{{\mathrm{O}}_2}$ kinetics were analyzed utilizing nonlinear regression. ${\dot{V}}_{{\mathrm{O}}_2}$ phase II amplitudes at the two cadences were similar in both groups. In healthy individuals, ${\dot{V}}_{{\mathrm{O}}_2}$_sc was steeper at 40 than 80 RPM (46.6 ± 12.0 vs. 29.5 ± 11.7 mL/min², p = 0.002) but not in COPD patients (16.2 ± 14.7 vs. 13.3 ± 7.6 mL/min²). End-exercise lactate concentration did not differ between cadences in either group. In healthy individuals, greater slow-cadence ${\dot{V}}_{{\mathrm{O}}_2}$_sc seems likely related to oxidative muscle fiber recruitment at higher muscular tension. COPD patients, known to have fast-twitch fiber predominance, might be unable to recruit oxidative fibers at high muscle tension, blunting ${\dot{V}}_{{\mathrm{O}}_2}$_sc response.

Keywords:

• ${\dot{V}}_{{\mathrm{O}}_2}$ slow component
• oxygen uptake
• heavy intensity exercise
• lactate
• pedaling rate
• chronic obstructive pulmonary disease
• cycle ergometer
• gas exchange

Declaration of Interest

All authors declare no conflicts of interest.

Additional information

Funding

R. Casaburi occupies the Grancell/Burns Chair in the Rehabilitative Sciences.